Python script to make all adjacent keyframes have constant interpolation
I don't think you need to write a script for that... If you want to set them to constant, just select them, press T and select "constant".
However, when you work with motion blur (and multiple shots overall), you should always create multiple cameras and switch between them: to do so, duplicate you active camera and place it in the spot you  want, in the timeline select the frame you want your cut to occur, press M to create a new marker (you can rename the marker if you like), then select the second camera and press CTRL-B, so that from that marker ahead the second camera will be the active one. 
This way you can have different settings between the 2 cameras without having to create useless keyframes and you won't have motion blur, because the camera doesn't jump in space to reach the new location (the blur you see is linked to the camera velocity, so even if the interpolation is constant you will always have some blurred frames when the camera jumps)